Grounded radial diode pack

ABSTRACT

The present disclosure relates to generators and their components. Specifically, a grounded radial diode pack is disclosed herein. A design to accommodate safe dissipation static charge build-up is disclosed. Safe dissipation of accumulated charge involves the provision of a suitable electrical path that will allow charges to flow to ground.

FIELD

The present disclosure relates to generators and their components, andmore particularly, to the interaction of a diode pack and generators.

BACKGROUND

Integrated Drive Generators (“IDG”) may supply constant frequency ACelectrical power to an aircraft. This may simplify the design of thecomplete electrical system of the aircraft. The IDG makes use of ahighly reliable continuously variable transmission (referred to as theconstant speed drive) which converts the variable input speed providedby an aircraft's engine into a constant output speed for the IDG'sintegral AC generator. A radial diode pack may be a component of theIDG.

SUMMARY

The present disclosure relates to a radial diode pack including anelectrically conductive oil transfer tube electrically coupled to anegative DC rail via an electrically conductive metal washer. Thepresent disclosure relates to a method of preventing static discharge ofa radial diode pack. The method may include coupling an electricallyconductive oil transfer tube of the radial diode pack to a groundingconnection.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present disclosure is particularly pointed outand distinctly claimed in the concluding portion of the specification. Amore complete understanding of the present disclosure, however, may bestbe obtained by referring to the detailed description and claims whenconsidered in connection with the drawing figures, wherein like numeralsdenote like elements.

FIG. 1 depicts a radial diode pack for use with an integrated drivegenerator in accordance with various embodiments;

FIG. 2 depicts a cross-sectional side view of the radial diode pack ofFIG. 1 in accordance with various embodiments;

FIG. 3 depicts a close up cross-sectional perspective view of the radialdiode pack of FIG. 2 in accordance with various embodiments;

FIG. 4 depicts a rotor circuit in accordance with various embodiments;and

FIG. 5 depicts a partial assembly drawing of an IDG in accordance withvarious embodiments.

DETAILED DESCRIPTION

The detailed description of exemplary embodiments herein makes referenceto the accompanying drawings, which show exemplary embodiments by way ofillustration and their best mode. While these exemplary embodiments aredescribed in sufficient detail to enable those skilled in the art topractice the disclosure, it should be understood that other embodimentsmay be realized and that logical changes may be made without departingfrom the spirit and scope of the disclosure. Thus, the detaileddescription herein is presented for purposes of illustration only andnot of limitation. For example, the steps recited in any of the methodor process descriptions may be executed in any order and are notnecessarily limited to the order presented. Furthermore, any referenceto singular includes plural embodiments, and any reference to more thanone component or step may include a singular embodiment or step.

The present disclosure relates to the design of a generator componentand more particularly, to the design of an integrated drive generator(IDG) radial diode pack. Aspects of the designs disclosed herein may beapplicable to other generators, such as a variable frequency generatorand/or an auxiliary generator. In general, a generator includes a stator(which functions as an exciter field) fixed relative to a housing and arotor (which functions as an exciter armature) rotatable about an axisrelative to the stator. The rotor includes a rotor frame carrying arotor circuit that includes field turns and a rectifier assembly. Therectifier assembly comprises at least one diode. Rotation of the rotorrelative to the exciter field induces an alternating current in theexciter armature turns, which is converted to a DC voltage by therectifier assembly.

Generators can experience rectifier assembly failures due to damageddiodes. One failure mode results from an electrostatic discharge eventbetween the rotor frame and an isolated rotor circuit. The rotor circuitis electrically insulated from the rotor frame. The isolation of therotor circuit can result in a buildup of a high voltage potential on therotor circuit relative to the rotor frame under common operationalparameters. The voltage potential built up within the isolated rotorcircuit discharges to the rotor frame when the voltage potential exceedsan insulation rating of the rotor frame. The voltage discharge canresult in a voltage across a diode in the rotor circuit that exceeds thediode voltage rating. This sudden voltage across the diodes results in areverse bias on each diode. The reverse bias may cause diode break downand/or a short in response to the voltage exceeding the diode voltagerating, thus damaging the rectifier assembly.

In accordance with various embodiments, a radial diode pack 10, shown inFIGS. 1 through 3. Radial diode pack 10 may be used in aerospaceapplications. Generally, oil cools radial diode pack 10. While notintending to be bound by theory, when a low conductivity liquid, e.g.,oil, flows past a solid surface, the liquid acquires a space charge dueto frictional charge separation at the liquid/solid interface. Ingeneral, ionic species of one sign are preferentially absorbed by thesolid, leaving a net charge of opposite sign in the liquid. The spacecharge developed in the liquid is transported by the flow, resulting ina streaming current or charging current being carried by the liquid. Ifthe walls of the flow system are insulated or floating, the flowelectrification process also leads to an electrostatic accumulation ofcharge and the generation of high electrostatic surface potential atliquid/solid interfaces.

With respect to diode failures, the location or “site” which experiencesthe charge accumulation is typically the electrical circuit within thegenerator rotor. The electrical circuit within the generator rotor isinsulated from the rotor shaft and floats electrically with respect tothe rotor shaft and other IDG components. Various elements of the rotorelectrical circuit come in contact with the oil stream in order tothermally cool the rotor. If the static charge of the rotor circuitreaches a high enough potential to break down the insulation system, anelectrostatic discharge between circuit and rotor shaft may occur. Thedischarge event is quick (typically, measured in nanoseconds), but canbe sufficiently strong to damage the diodes in the rotor circuit. Theenergy for this discharge event comes from the parasitic capacitanceprimarily between rotor circuit elements (windings) and rotor structure(slots). This capacitance is a “distributed” capacitance, but it is aneffective energy storage system nonetheless. Depending upon rotorconstruction, most or all of the static charge voltage will be forcedacross a main field winding and the rectifier. Voltages in excess of2000 Volts are typically required to break down the rotor circuitinsulation system, and this magnitude is beyond the capability ofcurrently used silicon diodes.

According to various embodiments, an approach to prevent static chargeaccumulation and the resulting discharge is to use materials and fluidsthat have fewer tendencies to generate static charge. This may beaccomplished through additives and/or an oil selected/fashioned toprevent static charge accumulation.

According to various embodiments, a design to accommodate static chargebuild-up is to provide a means for safe dissipation of the charge. Safedissipation of accumulated charge involves the provision of a suitableelectrical path that will allow charges to flow to ground.

The rotor circuit (exciter armature, diode assembly, and main field) iselectrically insulated from the rotor shaft. Stated another way, therotor circuit floats electrically with respect to the shaft. Anelectrical connection between the rotor shaft and a single point withinthe rotor circuit has no effect on generator performance, but cancontrol the level of voltage the rotor circuit can achieve with respectto the shaft. A direct connection (or ground) between the rotor circuitand shaft will fix that point of the rotor circuit to the shaftpotential. The potential between all other points of the rotor circuitand the shaft will be dictated by normal rotor circuit operation.Likewise, a resistive connection can be made between the shaft andcircuit. A resistive connection may hold rotor circuit voltage levelswith respect to the shaft low enough to prevent static discharge. Staticcharge accumulation on the rotor circuit will dissipate at relativelyhigh impedances.

Whether connected directly or through a resistive coupling, in suchconfiguration the rotor circuit does not achieve a potential sufficientto result in static discharge. Disclosed herein is a connection whichprovides a path for safe dissipation of the charge. Stated another way,by electrically coupling any singular point of the rotor circuit to theshaft, developing a potential on the rotor circuit relative to the shaftis negated. The highest potential achievable in the rotor circuitrelative to the shaft is merely the potential within that circuititself. Thus, the rotor circuit is prevented from reaching a level wherean electrical arc is likely.

According to various embodiments, and with renewed reference to FIGS. 2,3, and 5, a radial diode pack 10 is disclosed where a groundingconnection is achieved indirectly through a metal washer 150 coupled toan oil transfer tube 120 of the radial diode pack 10. Metal washer 150is conductive. Oil transfer tube 120 may be electrically and physicallycoupled to a second oil transfer tube 130. Second oil transfer tube 130may be electrically coupled to the metal housing 140. The metal housing140 is operatively and electrically coupled to a plurality of bearings170. The bearings may be operatively and electrically coupled to therotating rotor shaft 200. The metal washer 150 may be electricallycoupled to the negative DC rail 65, (associated with positive DC rail 60such as via an electrically conductive coupler 70.

Thus, in this embodiment, there is no grounding connection directly fromthe rotor circuit to the rotor shaft 200. The connection is indirectincluding a path through at least one oil transfer tube. FIG. 4 outlinesa high level representation of the rotor circuit. With this design,static charge accumulation and the resulting discharge to the diode packassembly that can cause the diodes to fail is prevented. Thus, the diodepack incorporates an electrical ground within the diode assembly thatprevents static charge build-up regardless of environmental conditionsand oil conductivity.

Benefits, other advantages, and solutions to problems have beendescribed herein with regard to specific embodiments. Furthermore, theconnecting lines shown in the various figures contained herein areintended to represent exemplary functional relationships and/or physicalcouplings between the various elements. It should be noted that manyalternative or additional functional relationships or physicalconnections may be present in a practical system. However, the benefits,advantages, solutions to problems, and any elements that may cause anybenefit, advantage, or solution to occur or become more pronounced arenot to be construed as critical, required, or essential features orelements of the disclosure. The scope of the disclosure is accordinglyto be limited by nothing other than the appended claims, in whichreference to an element in the singular is not intended to mean “one andonly one” unless explicitly so stated, but rather “one or more.”

Systems, methods and apparatus are provided herein. In the detaileddescription herein, references to “various embodiments”, “oneembodiment”, “an embodiment”, “an example embodiment”, etc., indicatethat the embodiment described may include a particular feature,structure, or characteristic, but every embodiment may not necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phrases are not necessarily referring to the same embodiment.Further, when a particular feature, structure, or characteristic isdescribed in connection with an embodiment, it is submitted that it iswithin the knowledge of one skilled in the art to affect such feature,structure, or characteristic in connection with other embodimentswhether or not explicitly described. After reading the description, itwill be apparent to one skilled in the relevant art(s) how to implementthe disclosure in alternative embodiments. Different cross-hatching isused throughout the figures to denote different parts but notnecessarily to denote the same or different materials.

Furthermore, no element, component, or method step in the presentdisclosure is intended to be dedicated to the public regardless ofwhether the element, component, or method step is explicitly recited inthe claims. No claim element herein is to be construed under theprovisions of 35 U.S.C. 112(f), unless the element is expressly recitedusing the phrase “means for.” As used herein, the terms “comprises”,“comprising”, or any other variation thereof, are intended to cover anon-exclusive inclusion, such that a process, method, article, orapparatus that comprises a list of elements does not include only thoseelements but may include other elements not expressly listed or inherentto such process, method, article, or apparatus.

What is claimed is:
 1. A method of preventing static discharge of aradial diode pack comprising: coupling an electrically conductive oiltransfer tube of the radial diode pack to a grounding connection; andelectrically coupling the electrically conductive oil transfer tube to asecond electrically conductive oil transfer tube.
 2. The methodaccording to claim 1, wherein the electrically conductive oil transfertube is housed within the radial diode pack.
 3. The method according toclaim 1, wherein the grounding connection is made via a negative DC railof the radial diode pack.
 4. The method according to claim 1, furthercomprising electrically coupling the electrically conductive oiltransfer tube to a metal washer.
 5. The method according to claim 1,further comprising electrically coupling the second electricallyconductive oil transfer tube to a metal housing.
 6. The method accordingto claim 5, further comprising electrically coupling the metal housingto a rotor shaft via a bearing.
 7. The method according to claim 1,wherein a rotor circuit associated with the grounding connection isprevented from reaching a level where an electrical arc will occur. 8.The method according to claim 1, wherein the radial diode pack isconfigured for use with an integrated drive generator.
 9. A radial diodepack comprising: a negative DC rail; an electrically conductive metalwasher; a first electrically conductive oil transfer tube; and a secondelectrically conductive oil transfer tube electrically coupled to thefirst electrically conductive oil transfer tube and to the negative DCrail via the electrically conductive metal washer.
 10. The radial diodepack of claim 9, wherein the negative DC rail is configured toaccommodate safe dissipation of built-up static charge via the metalwasher.
 11. The radial diode pack of claim 10, wherein the safedissipation of accumulated charge involves the provision of a suitableelectrical path allowing charges to flow to ground.
 12. The radial diodepack according to claim 10, wherein the second electrically conductiveoil transfer tube is electrically coupled the to a metal housing. 13.The radial diode pack according to claim 10, wherein a rotor circuitassociated with the radial diode pack is prevented from reaching a levelwhere an electrical arc will occur.